PREDISPOSING CAUSES 99 



house thoroughly coated with whitewash. This spraying and 

 whitewashing was repeated at frequent intervals during the fall. In 

 the early spring, after the snow had melted, he again thoroughly 

 raked up the pens and burned everything in the way of refuse that 

 was to be found. The pens were again treated with chlorid of 

 lime, and a new bunch of hogs were then brought in from an ad- 

 jacent county. These animals thrived first class in every respect, 

 and raised litters of strong healthy pigs. 



The neighboring farmer was not of the same industrious makeup 

 as his neighbor, and allowed his pens to remain untouched during 

 the winter, saying that the frost would kill out the disease. In the 

 spring he also secured a number of brood sows and placed them in 

 his pens. All went well for about three months, when his pigs 

 began to die again, and by the end of summer his hog lots had 

 again been swept clean by cholera. 



This goes to show both the persistency of the germs of cholera, 

 even through a cold winter, such as seen in Iowa, and also illus- 

 trates the effect of a little effort in the way of cleaning up in ridding j 

 premises of cholera. 



PREDISPOSING CAUSES 



In addition to this ultramicroscopic virus, which is the direct 

 or active cause of hog-cholera, we have a large number of other 

 factors which make the herd more liable to attack by the disease 

 — that is, make them more susceptible to cholera — and these in- 

 fluences are known as accessory or predisposing causes. These 

 are the conditions which cause the disease to appear in the herd of 

 one farmer and not in that of another which may be locating in 

 very close proximity to the infected farm. 



These predisposing or accessory causes are many, among the 

 most important of them being the following: 



(1) Age. — Cholera is a disease which may attack animals at 

 any age. Very young pigs may be attacked ; in fact, it is not un- 

 common to have the virus of this disease attack the pigs while 

 still unborn and in the uterus or pig-bag, with the result that they 

 are all killed and the sow aborts or slunks the entire litter. 



On the other hand, every farmer has observed that these old 

 sows, while they may become sick, appear unthrifty for a consider- 



